A fuel cell causes a hydrogen-containing fuel gas and an oxygen-containing oxidizing gas, such as air, to electrochemically react with each other to generate electric power and heat at the same time. The hydrogen-containing fuel gas is obtained by reforming a material gas, such as a city gas. A unit cell (cell) of the fuel cell includes: an MEA (Membrane-Electrode-Assembly) constituted by a polymer electrolyte membrane and a pair of gas diffusion electrodes; gaskets; and electrically conductive separators. A groove-like gas channel through which the fuel gas or the oxidizing gas (each of these gases is referred to as “reactant gas”) flows is formed on a main surface of the separator which surface contacts the gas diffusion electrode. The gaskets are disposed around a peripheral portion of the MEA, and the pair of separators sandwich the MEA. Thus, the cell is formed.
A common fuel cell is so-called a stack-type fuel cell in which the cells are stacked on and fastened to one another, and adjacent MEAs are electrically connected to each other in series. When manufacturing the cell stack, the stacked cells are sandwiched between end plates, and the end plates and the cells are fastened by fasteners. Therefore, the polymer electrolyte membrane needs to have an adequate strength so as to be able to endure the fastening pressure and not to be physically damaged by, for example, abrasion in a long-period use.
To such needs, known is a seal structure of a solid polymer electrolyte fuel cell in which a frame-shaped protective membrane is attached to the polymer electrolyte membrane (see Patent Document 1 for example).
FIG. 9 is a schematic diagram showing an outline of the seal structure of the solid polymer electrolyte fuel cell disclosed in Patent Document 1.
As shown in FIG. 9, a frame-shaped protective membrane 220 formed by a fluorocarbon resin-based sheet is disposed on a main surface of a solid polymer electrolyte membrane 210 such that an inner peripheral portion thereof is covered with an electrode 213. In addition, a gas sealing material 212 is disposed to surround the electrode 213 such that a gap 214 is formed between the gas sealing material 212 and the electrode 213. With this, since the protective membrane 220 is sandwiched between the gas sealing material 212 and the solid polymer electrolyte membrane 210 and between the electrode 213 and the solid polymer electrolyte membrane 210, and the protective membrane 220 reinforces the solid polymer electrolyte membrane 210 at the gap 214, the damage of the solid polymer electrolyte membrane 210 can be prevented without increasing the thickness of the solid polymer electrolyte membrane 210.    Patent Document 1: Japanese Laid-Open Patent Application Publication 5-21077